Help needed about bypass capacitor

karnalta:
My questions are :

  • Is it really useful to put a bypass capacitor on the other board just before the TIP transistor gate to ensure that the gate always receive a clean power ?

Doesn't hurt...

  • Does bypass capacitor are standard capacitor ? I mean I can use a normal ceramic capacitor ? Because I have seen some website selling specially named "bypass capacitor".

I am not an expert by any means in electronics, but I never heard of a capacitor that was just for bypassing..

  • To produce drops with the solenoid valve I have to put it on for short amount of time (like 50-60ms), then wait desired delay between drops and so on .. Would a capacitor apply lag to this process has it have to charge himself ? While it's charging the power won't reach the transistor gate, right ?

It shouldn't..

  • And the last one, how do I calculate the size of a bypass capacitor ? I am by example thinking to add one on the 12v DC of the solenoid as it is provided by a very old power supply.

Usually go for .01uF to 10 uF is a good number to start off. Maybe for higher voltages, 100uF...